1. Technical Field
The present invention relates to a novel optical compensation film useful for optical compensation of liquid crystal display devices, and a liquid crystal display device employing the same.
2. Background Art
A VA (vertically aligned)-mode liquid crystal display device has been known as a liquid crystal display device having wide viewing angle characteristics. The VA-mode liquid crystal display device is generally superior to liquid crystal displays of other modes in terms of high contrast, but suffers from large changes in contrast and color depending on viewing angle. In one known configuration aimed at solving this problem, polarizer plates are disposed on the upper and lower sides of a liquid crystal cell so as to align the absorption axes thereof orthogonal to each other, and an optically biaxial retardation film is further disposed between each of the polarizer plates and the liquid crystal cell, proving that degradation in the contrast depending on viewing angles may be reduced (see Japanese Examined Patent No. 3330574, for example).
It is, however, difficult to completely suppress leakage of light in the black state, when the pair of polarizer plates disposed while aligning the transmission axes orthogonal to each other are observed from oblique directions, because of displacement caused in the orthogonal relation between two transmission axes. Known proposals having been made on optical compensation films, capable solving this problems, include a biaxial retardation compensation film having predetermined wavelength dispersion characteristics of retardation in plane (Re) and retardation along the thickness direction (Rth) (see Published Japanese Translation of PCT International Publication for Patent Application No. 2006-515686, for example); and an optically biaxial optical compensation film showing a predetermined wavelength dispersion characteristic of Re/Rth (see Japanese Unexamined Patent Publication, “Tokkai” No. 2005-221962, for example).
While the VA-mode liquid crystal display devices were mentioned in the above, similar problems in the black state may occur also in TN-mode liquid crystal display devices. As a means for solving the problems, a proposal has been made on control of wavelength dispersion characteristics of Re and Rth of the optical compensation film.